docs: more cleanup following restructure (#2702)

- add TOC for Reference section
- make external links use _blank to open a new tab
- fix some more /gen links spots I missed, oops
- add a general redirect from old /gen links → /reference
- some more stylistic touchups

### Change Type

- [x] `documentation` — Changes to the documentation only[^2]

### Release Notes

- Docs: further cleanup following restructure.

apps/docs/scripts/functions/getApiMarkdown.ts

@@ -111,7 +111,7 @@ export async function getApiMarkdown(categoryName: string, item: ApiItem, j: num
 	await addFrontmatter(result, item, categoryName, j)
 
 	if (toc.markdown.length) {
-		result.markdown += `<details class="article__table-of-contents">\n\t<summary>Table of contents</summary>\n`
+		result.markdown += `<details className="article__table-of-contents">\n\t<summary>Table of contents</summary>\n`
 		addMarkdown(result, toc.markdown)
 		result.markdown += `</details>\n\n`
 	}